Potential for Anaerobic Digestion of Crop Residues Ron Fleming & Malcolm MacAlpine (Ridgetown Campus of University of Guelph), Jim Todd (OMAFRA) CSBE09-706

Funding OMAFRA – Alternative Renewable Fuels Plus program U of Guelph/OMAFRA Agreement

Objectives Suitability of various agricultural by-products, mainly related to vegetable production and processing, as feedstocks for AD Feedstock handling, processing and storage requirements Optimum conditions to maximize methane production Economic potential of using vegetable wastes as energy feedstocks Nutrient quality of digestate

Overview 3 year project – 2008 to 2010 Use a pilot scale anaerobic digester Potential in Ontario to use organic “waste” materials common in agriculture to produce energy through the use of an anaerobic digester ◦ Consider livestock manure as an input ◦ Look at crop residuals from various field crops

Top 10 Vegetable Crops for Marketed Production in Ontario

Example: Tomato Waste Available for 8 weeks – August/September Waste represents 3 to 13% of total harvested 3 types of processing wastes: ◦ Pomace (mostly skins) – 800 t in 2008 ◦ Lye sludge (+/- 94% water) and Screenings (stems, seeds, etc) – 16,000 to 19,000 t

Potential Biogas Yields Liquid cattle manure Liquid swine manure Fodder beets Grass Green maize, dough stage Corn silage, dough stage, high-grain Grass silage, first cut Corn silage, waxy stage, high-grain Food waste Potato mash, fresh Whey Potato peelings Silage from sugar beet leafs Brewer`s grain silage Skimmed grease Molasses Waste bread Canola cake, 15 % fat Waste grease Baking wastes (m 3 biogas/tonne)

Description of AD System 152 cm diameter, 130 cm depth, flexible domed top, total volume = 2.7 m 3 ; liquid volume = approx. 1.8 m 3 Complete-mixed mesophilic system

Mobile Anaerobic Digester

Feeding Hopper and Auger

Auger Tube Outlet

Mixing Paddle and Heating Coils

Electric and Heating Systems

Gas Analyzer and Flow Meter

Flare and Pressure Relief Tube

Test Method Various materials/mixtures tested Approx. 4 weeks for each recipe Daily Monday to Friday: ◦ Gas samples analyzed ◦ Gas volume recorded ◦ Gas flared ◦ Mixer started ◦ Material added

Loading rate Ranged from 0.5 to 1.2 kg VS/m3 digester capacity Average hydraulic retention time ranged from 21 to 40 days

Input #1 Sugar beets + swine manure

Adding mixture of sugar beets and manure to feed hopper

Input #2 Liquid swine manure Had been stored for several months Represents an input that is plentiful

Input #3 Sweet potatoes Chopped fine Added to digestate, mixed and added to digester as a slurry No new liquids added

Input #4 Sweet potatoes + (fresh) swine manure Digestate removed Sweet potatoes mixed with fresh swine manure

Input #5 Swine manure Freshly produced manure

Input #6 Dried tobacco Nicotine-free tobacco leaves (dry) Mixed with digestate before adding to digester as a slurry

Sample Analysis Biogas: ◦ Methane (CH 4 ), Carbon Dioxide (CO 2 ) Inputs and outputs: ◦ N, P, K, pH, NH 4 -N, C, ash ◦ Calculated C:N ratio ◦ Calculated Volatile Solids

Results for 2008

Example of Daily Inputs and Methane Production – Sweet Potatoes & Swine manure

Example of Cumulative Gas Production and VS Inputs – Sweet Potatoes & Swine manure

Sugar beets & swine manure – poor gas production – but – first test for the unit & problems with temperature control Fresh swine manure yielded twice as much methane as older swine manure Dried tobacco was the most difficult to mix Digestion led to a decrease in DM and an increase in NH 4 -N

InputBiogas Methane content Swine manure + sugar beets57% “Older” swine manure64% Sweet Potatoes48% Sweet Potatoes + manure56% “Fresh” swine manure63% Nicotine-free tobacco leaves49%

InputMethane Produced (L/kg VS) Swine manure + sugar beets233 “Older” swine manure336 Sweet Potatoes547 Sweet Potatoes + manure585 “Fresh” swine manure670 Nicotine-free tobacco leaves358

Advantages of this test setup Can change recipe fairly easily Don’t need huge quantities of inputs Is a good demonstration unit – technology transfer

Limitations Currently only able to add inputs 5 days per week A few design problems – e.g. input auger not sufficient for many materials – some re-design needed Initial difficulty keeping temperature constant – has been resolved Assumes gas production stabilized within 4 weeks

This year Continue testing – vegetable wastes + other farm organic materials Document logistical considerations for various materials Document economic considerations

Questions?